HSVtk protein expression profile of stable clones by western blot.

HSVtk protein expression levels of 4 stable clones, N2A-pCMV-HSVtk, U251-pCMV-HSVtk, N2A- pGFAP-HSVtk, and U251-pGFAP-HSVtk, at the 1st, 2nd, and 4th week were demonstrated by western blot and β–actin served as an internal control in all groups. The western blot images were quantified by ImageJ software (n = 3). (A) Before transfection, N2A parent cells showed no HSVtk expression level. After transfection and selection, the HSVtk expression levels of N2A-pCMV-HSVtk were stable within 4 weeks. Thus, N2A-pCMV-HSVtk was a stable clone and could be used for further experiments. (B) The U251 parent cells showed no HSVtk expression before transfection. U251-pCMV-HSVtk showed stable expression levels of HSVtk within 4 weeks and could be used as a control stable clone for glioblastoma. (C) HSVtk expression could not be detected in N2A-pCMV-HSVtk, since GFAP promoter was not activated in N2A cell line. (D) U251-pGFAP-HSVtk expressed HSVtk stably and continuously within 4 weeks. (TIF)